Carbon dioxide (CO2) contained in a piston–cylinder arrangement, initially at 6 bar and 400 K, undergoes an expansion to a final temperature of 298 K, during which the pressure–volume relationship is pV1.2 = constant. Assuming the ideal gas model for the CO2, determine the final pressure, in bar, and the work and heat transfer, each in kJ/kg.

Respuesta :

Explanation:

The given data is as follows.

          Initial temperature ([tex]T_{1}[/tex]) = 400 K

          Final temperature ([tex]T_{2}[/tex]) = 298 K

            Process [tex]P \nu^{1.2}[/tex] = C

For [tex]CO_{2}[/tex], according to the properties of various substances the values are as follows.

          R = 0.1889 kJ/kg K

       [tex]C_{p}[/tex] = 0.846 kJ/kg K

Therefore, calculate the final pressure as follows.

         [tex]\frac{P_{2}}{P_{1}} = (\frac{T_{2}}{T_{1}})^{\frac{n}{n-1}}[/tex]

         [tex]\frac{P_{2}}{6} = (\frac{298}{400})^{\frac{1.2}{1.2-1}}[/tex]

            [tex]P_{2}[/tex] = 1.025 bar

Hence, final pressure is 1.025 bar.

Now, work done will be calculated as follows.

             W = [tex]\frac{P_{1}\nu_{1} - P_{2}\nu_{2}}{n - 1}[/tex]

                 = [tex]\frac{m(RT_{1} - RT_{2})}{n - 1}[/tex]

                 = [tex]\frac{1 \times 0.1889(400 - 298)}{(1.2 - 1)}[/tex]

                 = 96.339 kJ/kg

Hence, work done is equal to 96.339 kJ/kg.

Formula to calculate the change in internal energy is as follows.

             [tex]\Delta U = C_{v}(T_{2} - T_{1})[/tex]

                         = 0.657 (298 - 400)

                         = -67.014 kJ/kg

Now, transfer of heat will be calculated as follows.

                 Q = [tex]\Delta U + W[/tex]

                     = -67.014 kJ/kg + 96.339 kJ/kg

                     = 29.325 kJ/kg

Therefore, amount of heat transfer is 29.325 kJ/kg.